In comparison the \(2\Leftrightarrow 2\)  reactions have a significantly higher reaction threshold when strangeness is produced and thus certainly are negligible near to strangeness freeze-out condition and associated chemical nonequilibrium we are interested in. On the other hand, these reactions are important near to the QGP hadronization temperature \(T\simeq 150\)  MeV and play an important part in the study of the evolution of strangeness in the HG phase emerging in QGP hadronization. However, there is no experimental scattering data available allowing the precise characterization of such reactions, instead one relies on theoretical concepts and models. For an introduction to this very different physics domain and detailed discussion of the here relevant reaction \(KK\leftrightarrow \pi \pi \)  we refer the reader to the Chapter 18 in Ref.[1]}.
